A multi-axis imaging system employing an array of optical imaging elements is a recent development. Adapted for microscopy, the array is miniaturized to form a miniature microscope array of objectives (“microscope array”), each objective having its own optical axis and typically including a number of the optical imaging elements.
Image data are recorded using light-sensing elements such as CCD arrays associated with each objective. The optical elements are spaced a predetermined distance from one another, and the entire array and object are moved relative to one another so that the positional relationship between image data from the detectors is fixed and data are thereby automatically aligned, eliminating the need for what is known in the art as “tiling.”
Another advantage of the multi-axis imaging system is its speed. An entire specimen can be imaged in one pass because the field of view (FOV) of the system can be arbitrarily large without sacrificing resolution.
Integrated circuit manufacturing processes include photolithographically defining circuit or other features on semiconductor wafers. These features include areas over which the wafer is doped and areas over which oxide and metal layers are deposited, to define and interconnect circuit structures. All of these areas are defined by photographic masks that are used in a projection imaging system to project light through the mask onto a wafer to which has been applied a photosensitive coating known in the art as photoresist. The mask includes open or light transmissive portions through which light passes into the photoresist and exposes the photoresist. The mask also includes closed or light opaque portions through which light is blocked from exposing the photoresist.
In a developing step of the process, photoresist that has been exposed to the light is removed while photoresist that has not been exposed to the light is not removed, or the reverse, depending on the whether the photoresist is positive or negative. Where photoresist remains after developing, it acts as a mask in subsequent processing; for example, for ionic implantation of dopants into the wafer, the ions are stopped from being implanted in the wafer where there is photoresist on the wafer. However, the ions are not stopped from being implanted where there is no photoresist on the wafer.
A mask defining a feature pattern for one die on a wafer may be stepped in rows and columns across the wafer to expose the wafer for all of the large number of die that can be formed from the wafer. However, this process is time-intensive and mechanically complex. Alternatively, a very large objective can be used with a large mask that defines the pattern for all the die on the wafer. However, it is desirable to increase the size of the wafers as much as possible to maximize economy of scale, and wafer size has steadily increased over time. For large diameter wafers, a correspondingly large objective is required to maintain high resolution, and the lenses used in such objectives are very expensive. The same problem arises whenever a large, high resolution image is to be projected.
Accordingly, there is a need for a multi-axis projection imaging system, for use in integrated circuit manufacture and for other uses as well.